In some integrated circuit (IC) applications it is desirable to have a mode in which the system clock frequency can be increased by a predefined amount on a temporary basis and then allowed to return to the original frequency (this mode is referred to herein as a Turbo Mode). For example, a switching system might experience a temporary increase in usage such that the overall performance of the communication network would be negatively impacted. If the IC could temporarily increase the frequency of its system clock, the network performance degradation might be avoided.
Conversely, in some applications it may be desirable to have a mode in which the system clock frequency can be decreased by a predefined amount on a temporary basis and then allowed to return to the original frequency (this mode is referred to herein as a Downshift Mode). For example, in the switching system described above, the traffic level might decrease to a point where a decrease in system clock frequency would reduce power consumption but still support the communication traffic.
A need therefore exists for methods and apparatus for deriving an integrated circuit clock signal with a frequency that is offset from the system clock